Could be from the wheel alignment because you have to turn the wheel from centre to different angles when the car is off, to check caster, to out on turns etc. As they were turning the wheel the p/s pump may have sucked in some air, due to low fluid or other problems. Try with the car off turning the wheel from lock to lock 10 or so times, checking p/s level and top it up if it drops down, that may help bleed air out of your steering